In the middle of this financial crisis there is a debate taking place over whether governments can afford both massive tax-funded spending programmes needed to revive ailing economies, and the emissions cuts that are needed to combat climate change.

Few regions on Earth throw this tension into sharper contrast than south-east Asia, where many nations are highly vulnerable to the effects of global warming while also having the chance to develop low-carbon economies.

The plain truth is that nations can no longer afford to delay action on climate change, even temporarily, and such spending can serve as effective fiscal stimulus. Despite the global economic downturn the world is still warming. A major new report from the Asian Development Bank – The Economics of Climate Change in Southeast Asia: A Regional Review – explains how countries that invest now in climate change adaptation will better protect their people, economy and environment. Even with aggressive adaptation efforts, the negative impacts of climate change will continue to worsen. Only concerted global action to reduce greenhouse gas emissions can ultimately steer the world off its current calamitous course.

The report examines a wide range of climate change impacts in Indonesia, Philippines, Singapore, Thailand and Vietnam. It finds a "business as usual" approach will result in a difficult future for the region and its people.

By the end of this century temperatures in south-east Asia will rise significantly, tens of millions will experience water shortages, rice production will decline, and large swaths of forests will disappear. Rising sea levels will force the relocation of millions of island dwellers and coastal communities, and there will be a surge in dengue, malaria and other diseases.

With population centres and economic activity concentrated along south-east Asia's coastlines and livelihoods particularly dependent on agriculture, fishing and natural resources, the region is acutely vulnerable. Adopting a similar modelling approach to that used in the 2007 Stern Review, the report concludes the region is twice as economically vulnerable to climate change compared with the rest of the world.

The good news is that far from the world's policy makers being captive to the economic crisis, the opposite is true: the crisis may offer opportunities if we can boost programmes to improve water, sanitation, climate-proofing and reduce carbon dependency and protect forests.

At their recent London Summit, G20 leaders agreed that current stimulus programmes should be used to foster a green, sustainable recovery. As was outlined in the recent joint report from the UK's Grantham Research Institute on Climate Change and the Environment and the Centre for Climate Change Economics and Policy – an outline of the case for a "green" stimulus – energy efficient and low carbon technologies are not simply means for reducing carbon emissions. They are also extremely effective as a fiscal stimulus because they can be implemented quickly and are relatively labour intensive.

For Asia's governments, these kinds of public investments, in both adaptation and mitigation, will be essential to eradicating extreme poverty, achieving the Millennium Development Goals, and making structural transformations that are needed to place the region on a low-carbon path.

Over the next 50 years, much of the world's new energy and urban infrastructure will be built in Asia, locking in the region's greenhouse gas emission pattern. Encouragingly, there are vast, untapped opportunities for energy efficiency improvements, cleaner transport, and for increasing the use of renewable energy sources including biomass, solar, wind, hydro and geothermal.

Some of these schemes can be financed through the government's own fiscal stimulus programmes, others with international assistance, including both additional funding sources and the transfer of knowledge and technologies.

That might seem like a lot to ask in the midst of the worst financial crisis since the Great Depression. But the benefits will be enormous.

We have no time to delay. The financial crisis will come to an end. Without action, the same cannot be said for climate change.

• Lord Stern is chairman of the Grantham Institute for Climate Change and the Environment and the IG Patel professor of economics and government at the London School of Economics. Haruhiko Kuroda is president of the Asian Development Bank.